It is proposed to study the biosynthesis of phenazine-l-carboxylic acid and iodinin (phenazine-1, 6-diol-5, 10-dioxide) by feeding labeled phenazine-1, 6-dicarboxylic acid and 6-C13-shikimic acid. The phenazine-1, 6-dicarboxylic acid is made from 2-chloro-3-nitrobenzoic acid and C14-carboxyl- m-aminobenzoic acid via the corresponding substituted diphenylamine. 6-C13- shikimic acid is made from 2-C13-acetic acid via 3-C13-pyruvic acids, which, in an enzymatic reaction, is coupled to erythrose-4-phosphate and ring closed. The isolated C13-labeled metabolites are to be converted into phenazine- l-methyl carboxylate and phenazine-1, 6-diol respectively. The C13-spectra of these compounds have been measured and assigned so that C13-enriched carbons can be identified.